Post-translational modification of arginine residues by methylation is important for many critical cellular processes including chromatin remodeling, gene transcription, protein translation, signal transduction, RNA splicing and cell proliferation. Arginine methylation is catalyzed by protein arginine methyltransferase (PRMT) enzymes. There are nine PRMT members in all, and eight have reported enzymatic activity on target substrates.
The protein arginine methyltransferase (PRMT) family of enzymes utilize S-adenosyl methionine (SAM) to transfer methyl groups to arginine residues on target proteins. Type I PRMTs catalyze formation of mono-methyl arginine and asymmetric di-methyl arginines while Type II PRMTs catalyze mono-methyl arginine and symmetric di-methyl arginines. PRMT5 is a Type II enzyme, twice transferring a methyl group from SAM to the two ω-guanidino nitrogen atoms of arginine, leading to ω-NG, N′G di-symmetric methylation of protein substrates.
PRMT5 protein is found in both the nucleus and cytoplasm, and has multiple protein substrates such as histones, transcription factors and spliceosome proteins. PRMT5 has a binding partner, Mep50 (methylosome protein 50) and functions in multiple protein complexes. PRMT5 is associated with chromatin remodeling complexes (SWI/SNF, NuRD) and epigenetically controls genes involved in development, cell proliferation, and differentiation, including tumor suppressors, through methylation of histones (Karkhanis, V. et al., Versatility of PRMT5 Induced Methylation in Growth Control and Development, Trends Biochem Sci 36(12) 633-641 (2011)). PRMT5 also controls gene expression through association with protein complexes that recruit PRMT5 to methylate several transcription factors p53 (Jansson, M. et al., Arginine Methylation Regulates the p53 Response, Nat. Cell Biol. 10, 1431-1439 (2008)); E2F1 (Zheng, S. et al., Arginine Methylation-Dependent Reader-Writer Interplay Governs Growth Control by E2F-1, Mol Cell 52(1), 37-51 (2013)); HOXA9 (Bandyopadhyay, S. et al., HOXA9 Methylation by PRMT5 is Essential for Endothelial Cell Expression of Leukocyte Adhesion Molecules, Mol. Cell. Biol. 32(7):1202-1213 (2012)); and NFκB (Wei, H. et al., PRMT5 dimethylates R30 of the p65 Subunit to Activate NFκB, PNAS 110(33), 13516-13521 (2013)). In the cytoplasm, PRMT5 has a diverse set of substrates involved in other cellular functions including RNA splicing (Sm proteins), golgi assembly (gm130), ribosome biogenesis (RPS10), piRNA mediated gene silencing (Piwi proteins) and EGFR signaling (Karkhanis, 2011).
Additional papers relating to PRMT5 include: Aggarwal, P. et al., (2010) Nuclear Cyclin D1/CDK4 Kinase Regulates CUL4B Expression and Triggers Neoplastic Growth via Activation of the PRMT5 Methyltransferase, Cancer Cell 18: 329-340; Bao, X. et al., Overexpression of PRMT5 Promotes Tumor Cell Growth and is Associated with Poor Disease Prognosis in Epithelial Ovarian Cancer, J Histochem Cytochem 61: 206-217 (2013); Cho E. et al., Arginine Methylation Controls Growth Regulation by E2F1, EMBO J. 31(7) 1785-1797 (2012); Gu, Z. et al., Protein Arginine Methyltransferase 5 Functions in Opposite Ways in the Cytoplasm and Nucleus of Prostate Cancer Cells, PLoS One 7(8) e44033 (2012); Gu, Z. et al., Protein Arginine Methyltransferase 5 is Essential for Growth of Lung Cancer Cells, Biochem J. 446: 235-241 (2012); Kim, J. et al., Identification of Gastric Cancer Related Genes Using a cDNA Microarray Containing Novel Expressed Sequence Tags Expressed in Gastric Cancer Cells, Clin Cancer Res. 11(2) 473-482 (2005); Nicholas, C. et al., PRMT5 is Upregulated in Malignant and Metastatic Melanoma and Regulates Expression of MITF and p27(Kip1), PLoS One 8(9) e74710 (2012); Powers, M. et al., Protein Arginine Methyltransferase 5 Accelerates Tumor Growth by Arginine Methylation of the Tumor Suppressor Programmed Cell Death 4, Cancer Res. 71(16) 5579-5587 (2011); Wang, L. et al., Protein Arginine Methyltransferase 5 Suppresses the Transcription of the RB Family of Tumor Suppressors in Leukemia and Lymphoma Cells, Mol. Cell Biol. 28(20), 6262-6277 (2008).
PRMT5 is overexpressed in many cancers and has been observed in patient samples and cell lines including B-cell lymphoma and leukemia (Wang, 2008) and the following solid tumors: gastric (Kim 2005) esophageal (Aggarwal, 2010), breast (Powers, 2011), lung (Gu, 2012), prostate (Gu, 2012), melanoma (Nicholas 2012), colon (Cho, 2012) and ovarian (Bao, 2013). In many of these cancers, overexpression of PRMT5 correlated with poor prognosis. Aberrant arginine methylation of PRMT5 substrates has been linked to other indications in addition to cancer, such as metabolic disorders, inflammatory and autoimmune disease and hemaglobinopathies.